If you're talking about this tool: https://www.generatebanners.com/free-open-graph-image-generator then there is no way to add line breaks indeed.
However if you do log-in into https://www.generatebanners.com/ then this feature is available (using the logged-in version is also free and much more complete than the simple demo).

How would you add the line breaks?

I had typed in something like "What do you need your audio and video to do? We'll Make it do that!" - It broke it into "What do you need your audio" "and video to do? We'll" Then the next line "Make It Do That" - That's not verbatim, but it gives the point. "We'll Make It Do That" should all have been on the separate line